Bit depth refers to the number of bits used to hold a pixel. Sometimes also referred to as “color depth” and/or “pixel depth”, bit depth determines the maximum number of colors that can be displayed at one time. In recent years, digital images and digital videos (hereinafter collectively referred to as “digital images”) with a bit depth greater than eight are more and more desirable in many application fields, including, but not limited to, medical image processing, digital cinema workflows in production and postproduction, and home theatre related applications.
Bit-depth scalability is potentially useful regarding the fact that at some time in the future, conventional eight bit depth and high bit depth digital imaging systems will simultaneously exist in marketplaces.
There are several ways to handle the coexistence of an 8-bit video and a 10-bit video. In a first solution, only a 10-bit coded bit-stream is transmitted and the 8-bit representation for standard 8-bit display devices is obtained by applying tone mapping methods to the 10-bit presentation. Tone mapping is a well-known technique to convert a higher bit depth to a lower bit depth, often to approximate the appearance of high dynamic range images in media with a more limited dynamic range. In a second solution, a simulcast bit-stream that includes an 8-bit coded presentation and 10-bit coded presentation is transmitted. It is the decoder's preference to choose which bit-depth to decode. For example, a 10-bit capable decoder can decode and output a 10-bit video while a normal decoder supporting only 8-bit video can just output an 8-bit video. The first solution is inherently incompliant with the 8-bit profiles of the International Organization for Standardization/International Electrotechnical Commission (ISO/IEC) Moving Picture Experts Group-4 (MPEG-4) Part 10 Advanced Video Coding (AVC) standard/International Telecommunication Union, Telecommunication Sector (ITU-T) H.264 Recommendation (hereinafter the “MPEG-4 AVC Standard”). The second solution is compliant to all the current standards but requires more overhead.